Heavy oil is the petroleum with API gravity lower than 20 (its density is higher than 0.932 g/cm3 at the temperature of 20° C.), generally comprising heavy crude oil, oil sand bitumen and residue. As the heavy crude oil and the oil sand bitumen have high density, high viscosity and high freezing point, they will lose flowability at ambient temperature or even higher temperature, and cannot be transported and processed like conventional crude oil. Particularly, the extra heavy oil and the oil sand bitumen with API gravities lower than 10 need to be blended with diluent or to be converted to light fraction, so as to form synthetic oil, which is then transported to a refinery to be processed. Therefore, the research and development of light fraction conversion and processing technology for the heavy oil is always a topic attracting wide interest in the industry.
One of the most important technologies of the heavy oil processing is the secondary upgrading for oil products. With the thermal reaction treatments of heavy oil components, for example, heavy oil hydrotreating, the hydrotreating of coking products, partial thermal cracking of heavy distillate products, etc., the upgraded products of the heavy oil (upgraded oil or synthetic oil) can be obtained. The secondary upgrading is beneficial for solving the stability problem of the thermal reaction products and removing impurities (such as sulfur and so on) in crude oils, thus obtaining the synthetic oil being more clean and stable and with increased APT gravity. The upgraded oil or the synthetic oil has good flowability, which can be easily transported to a refinery; in addition, the impurities, asphaltenes, metals and carbon residue precursors in the treated upgraded oil are removed significantly, thus improving the quality of the oil and also convenient for the subsequent oil processing.
The key heavy components influencing the quality of the heavy oil are asphaltenes and metal, therefore, the deasphalting process is also an important step for converting the heavy oil to light oil. As for the heavy oil process, the de-asphalted oil with good properties can be obtained from the heavy oil through a solvent deasphalting process. However, the selection of the extraction solvent and the determination of the operating parameters for extraction process are greatly restricted by the properties of asphalt, which has the characteristics of high softening point, high viscosity and easily forms coke by heating. The existing problems firstly are that the asphalt with high softening point and the solvent are difficult to be separated that it is difficult to increase yield of de-asphalted oil, and secondly are that hard asphalt is difficult to be transported because of its high viscosity and easily forms coke by heating. Under the restrictions of these technical problems, the oil yield of the de-asphalted oil process for heavy oil, extra heavy oil and oil sand bitumen is low and a large quantity of asphalt needs to be processed or utilized in other proper ways, during the solvent deasphalting process currently.
In order to improve the heavy oil processing, combined processes with various matching designs are disclosed and utilized. Their purposes are all that: through more than two combined treatment processes, the heavy oil is processed and upgraded more effectively, improving its API gravity and producing the corresponding upgraded oil (it is also called as synthetic oil). In some combined processes, the de-asphalted oil and de-oiled asphalt are obtained through the solvent deasphalting process, which is a necessary process for various combined processes, such as the combined process of the solvent deasphalting process and delayed coking process, the combined process of the solvent deasphalting process and hydrotreating process, and so on. For example, Europe Patent No. EP1268713(A1) discloses a process for upgrading heavy oil feedstock. By using the solvent deasphalting process, the de-asphalted oil and the de-oiled asphalt are obtained and respectively subjected to slurry-bed hydrocracking. The upgraded oil and the unreformed asphalt are separated from hydrotreating products. The asphalt with the boiling point more than 1025° F. can be taken as coked feedstock and POX gasification feedstock. U.S. Pat. No. 6,673,234 discloses a combined process of initial solvent deasphalting process followed by delayed coking process. After the residual oil is treated in the solvent deaspholting process, the de-asphalted oil obtained is processed in the delayed coking, which can lengthen coking cycle time and produce needle coke. In the combined process, which has been used or disclosed, involving solvent deasphalting processes, it is necessary to separate the solvent in the de-oiled asphalt. That is, solvent needs to be separated from de-oiled asphalt firstly and, then, the de-oiled asphalt enters the sequent combined process. Therefore, the two problems associated with the asphalt with high softening point and the solvent are difficult to be separated from each other during the solvent deasphalting process and the asphalt with high softening point is hard to be transported are not solved. On the other hand, currently, as for the heavy oil process technology, the difficulty of the separation of the de-oiled asphalt from the solvent is reduced at the cost of lowering the yield of de-asphalted oil, thus increasing the quantity of de-oiled asphalt. As the oil component in the asphalt is relatively high, the quantity of coke produced in cocking process after the thermal reaction of the asphalt is also increased; that is, the amount of the coke and the gas are difficult to be decreased. Still on the other hand, in order to reduce the difficulty of separation of solvent from the asphalt with high softening point and the difficulty of transporting of the asphalt with high softening point, the oil component residues in the de-oiled asphalt is relatively high. During the thermal cracking process, part of the oil component undergoes condensation reaction, and then the quantity of coke in the thermal reaction is necessarily increased, thus influencing not only the liquid yield but also the stability of the upgraded products.